This invention relates to alarms that indicate undesired vehicle movement.
Various alarms have been devised to warn people that a vehicle has moved in general or drifted from a desired location, For example, U.S. Pat. No. 3,217,291 to King, U.S. Pat. No. 3,418,627 to Lyons and U.S. Pat. No. 3,690,285 to Ellison show drift indicators for anchored boats.
While these devices are adequate for indicating that a boat has drifted too far from its mooring, they are cumbersome and somewhat complex. Perhaps that is why their general concept has not been applied to indicate and thereby prevent a similar problem in the trailer truck industry--namely, a common cause of accidents at loading docks, known as "trailer creep".
That is when a trailer inches forward, separating from a loading dock. Often, the movement is slow and undetected until it is too late. When that happens, the loading bridge between the trailer and dock falls. If a person or forklift operator is on the bridge, down he goes, and the results can be disastrous.
Dock safety systems have been designed to try to prevent this problem. For example, wheel chocks are sometimes placed under a truck's wheels. While these chocks normally prevent the trailer from creeping, they have definite drawbacks: they sometimes slip under the wheels and allow undetected motion; they must be positioned precisely under the wheels to be effective; they require personnel to leave a dock platform to install them under the wheels; they are heavy and cumbersome to carry; and, if they are forgotten and not removed prior to a truck leaving the dock, they can be run over, with the result being damage to the truck or its cargo.
A more sophisticated system has recently been developed to stop trailers and trucks from creeping. It is called the DOK-LOK.RTM., produced by the Rite-Hite Corporation of Milwaukee, Wis.
The DOK-LOK.RTM. is a large safety unit that is permanently mounted onto a loading dock. The unit has a movable clamp that can be hooked onto a docked trailer's "I.C.C. bar". When engaged, the clamp firmly holds the bar and keeps the trailer from moving.
While the DOK-LOK.RTM. works, it too has drawbacks. Specifically, the unit is relatively expensive and difficult to install; it requires extensive maintenance; it requires the docked trailer to have an undamaged I.C.C. bar in order to function; and, it can cause damage to the attached truck or dock if it is not disengaged before the truck "pulls away" from the dock.
Accordingly, it is a primary object of the present invention to prevent dock accidents caused by trailer creep, but by a simpler means than heretofore seen.
It is a general object to provide a simple movement detector which will automatically provide an alarm and alert personnel in a loading area that a trailer is moving or creeping forward so that steps can be taken to arrest the trailer before damage or injury is incurred.
It is a more specific object to provide a compact creep alarm that can be easily installed onto a dock, wherein the unit has a spring-loaded, spool-fed cord that can be easily attached to a docked trailer, by either a clamp or magnetic plate. If the trailer creeps after the alarm is "armed", it tugs the cord, which triggers the alarm.
It is another object to provide an automatic creep alarm that will automatically arm itself after a retractable cord is pulled from the alarm's housing and clamped onto a trailer or truck.
It is a further object to provide a creep alarm that is inexpensive to manufacture, yet extremely durable and safe to use.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.